Perforator charge having an energetic material

ABSTRACT

A perforator charge includes a case, an explosive inside the case, and a liner to be collapsed by detonation of the explosive to form a perforating jet. The perforator charge also includes an energetic material to be activated in response to the detonation of the explosive.

BACKGROUND

To complete a well for purposes of producing fluids (such as hydrocarbons or other fluids) from a reservoir, or injecting fluids into the reservoir, one or more zones in the well are perforated to allow for fluid communication between a wellbore and the reservoir. Perforation is accomplished by lowering a perforating gun to a target interval within the well. Activation of the perforating gun creates openings in any surrounding casing or liner and extends perforation tunnels into the surrounding subterranean formation.

SUMMARY

In general, according to some implementations, a perforator charge includes a case, an explosive inside the case, and a liner to be collapsed by detonation of the explosive to form a perforating jet. The perforator charge also includes an energetic material to be activated in response to the detonation of the explosive.

Other or alternative features will become apparent from the following descriptions, from the drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Some embodiments are described with respect to the following figures:

FIG. 1 illustrates an example tool string having a perforating gun with perforator charges according to some implementations;

FIGS. 2A and 2B are cross-sectional views of perforator charges according to various implementations;

FIG. 3 is a sectional view of the perforator charge of FIG. 2A;

FIG. 4 is a cross-sectional view of a perforating gun having a perforator charge according to alternative implementations; and

FIG. 5 is a flow diagram of a process of using a perforator charge according to some implementations.

DETAILED DESCRIPTION

A perforating gun that is used for creating perforation tunnels in the surrounding subterranean formation can include a carrier structure and a number of perforator charges mounted to the carrier structure. In some examples, the carrier structure can be a loading tube that contains perforator charges. Alternatively, the carrier structure can be a strip carrier that is generally shaped as a strip, onto which perforator charges can be mounted.

The explosive nature of creating perforation tunnels in the subterranean formation can create a crushed zone in the formation. A “crushed zone” refers to a damaged zone that surrounds a perforation tunnel, where the perforating action has altered the formation structure and its permeability. Also, the perforating action can cause debris to fill perforation tunnels. The crushed zone damage can result in reduced ability to perform production or injection.

In accordance with some embodiments, a perforator charge is provided with an energetic material (in addition to a main explosive in the perforator charge) to produce a relatively high energy wave (such as in the form of a relatively high pressure pulse or an explosive blast) that can result in creating fractures in the subterranean formation, enlargement of a perforation tunnel, and/or removal or reduction of crushed zone damage in the formation. The energetic material is activated in response to detonation of the main explosive in the perforator charge.

FIG. 1 illustrates a tool string 100 that is lowered into a wellbore 102. The wellbore 102 can be lined with casing or liner 104. The tool string 100 is lowered on a deployment structure 106, which can be a wireline, tubing (e.g. coiled tubing or other tubing), a pipe, and so forth. The tool string 100 has a perforating gun 108, which includes a carrier structure 110 to which perforator charges 112 are attached. In some implementations, the carrier structure 110 can be a loading tube defining an inner chamber (which can be sealed from outside well fluids) in which the perforator charges 112 are mounted. Alternatively, the carrier structure 110 can be a strip onto which the perforator charges 112 are mounted. In other examples, the carrier structure 110 can have other forms.

In the ensuing discussion, reference is made to implementations where the carrier structure 110 is a loading tube. Note that techniques or mechanisms according to some embodiments can be applied to other types of carrier structures.

The perforator charges 112 are ballistically connected to a detonating cord 114. Initiation of the detonating cord 114 causes detonation of the perforator charges 112.

The detonating cord 114 can be connected to a firing head 116, which can be activated from an earth surface 118, such as by use of equipment at the earth surface 118. The activation of the firing head 116 can be in response to electrical commands, acoustic commands, pressure commands, optical commands, and so forth, that can be sent from the equipment at the earth surface 118 to the firing head 116. Alternatively, the activation of the firing head 116 can be performed mechanically.

FIG. 2A is a cross-sectional view of an example perforator charge 112, which includes an outer case 202 that acts as a containment vessel designed to hold the detonation force of the explosion of the perforator charge 112 for a length of time to allow for a perforating jet to form. The outer case 202 can be formed of a metal, such as steel, or some other material. A main explosive 204 is contained inside the outer case 202. The main explosive 204 is sandwiched between the inner wall of the outer case 202 and a surface of a liner 206.

In some examples, the liner 206 is generally conically shaped. As a result of the general conical shape of the liner 206, the main explosive 204 is also generally conically shaped between an inner wall of the outer case 202 and the liner 206. In other examples, the liner 206 can be generally bowl-shaped or have a parabolic shape.

In examples according to FIG. 2A, a rear portion of the outer case 202 has an opening 208, which can be in the form of a semi-circular slot or a slot having another shape. The opening 208 allows an end portion 210 of the main explosive 204 to be ballistically contacted to a primary explosive, such as the detonating cord 114 shown in FIG. 1. The detonating cord 114 is not shown in FIG. 2A, but is shown in FIG. 1 and in FIG. 4 (discussed further below).

In some examples, a retaining element 212 is attached (e.g. glued, welded, or otherwise attached) to the outer case 202. The retaining element 212 can be a retaining wire, for example, which is bendable for holding the detonating cord 114 against the rear portion 210 of the main explosive 204. In other examples, the retaining element 212 can be another type of retaining element, or alternatively, the retaining element 212 can be omitted.

According to some embodiments, the perforator charge 112 further has an energetic material 214, which is placed at a front portion of the perforator charge 112. The “front portion” of the perforator charge 112 is the portion of the perforator charge 112 through which the perforating jet extends upon detonation of the perforator charge 112. Stated differently, the “front portion” of the perforator charge 112 is at the front opening of the outer case 202, through which the perforating jet passes.

The energetic material 214 is a material that when activated causes production of an energy wave, such as a pressure pulse, an explosive blast, and so forth. In some implementations, examples of the energetic material 214 include a propellant, a high explosive, gun powder, a combustible metallic powder (e.g. aluminum powder, magnesium powder, manganese powder, copper powder, zinc powder, titanium powder, iron powder, sodium powder, potassium powder, nickel powder, chromium powder, etc.), thermite (a mixture of aluminum powder and a metal oxide, for example), or any combination of the foregoing. In more specific implementations, examples of the energetic material 214 include a high explosive, gun powder, thermite, or any combination of the foregoing. In other implementations, other types of energetic materials can be used.

The energetic material 214 is generally a discrete segment formed of the energetic material that is placed at the front portion of the perforator charge 112. A “discrete segment” of energetic material can refer to any layer, piece, or other amount of the energetic material that has a predefined extent such that the energetic material does not surround an outer surface 203 of the outer cover 202. In some examples, the discrete segment of energetic material 214 does not contact any part of the outer surface 203 of the outer cover 202.

The energetic material 214 is retained to the outer case 202 of the perforator charge 112 using a retaining structure that is attached to the outer case 202. In some implementations, the retaining structure can be a retaining shell (or retaining cap) 216 that covers the discrete segment of energetic material 214. The retaining shell 216 has a receiving chamber 218 in which the energetic material 214 is positioned. The retaining shell 216 is attached to the outer case 202 (at 217). The attachment can be a threaded connection between the retaining shell 216 and the outer case 202. Alternatively, the retaining shell 216 can be attached to the outer case 202 using another type of attachment mechanism, such as by use of a screw, a rivet, glue, and so forth.

In examples according to FIG. 2A, the retaining shell 216 has a protruding portion 220 that extends into an inner opening 215 (shown in FIG. 3) of the energetic material 214. FIG. 3 is a sectional view of the energetic material 214, which is generally ring-shaped and has the inner opening 215 formed in the energetic material 214. The energetic material 214 is “generally” ring-shaped in that the energetic material 214 has a shape resembling a ring—note that manufacturing or design tolerances can cause the energetic material 214 to not have an exact ring shape.

In different implementations, rather than providing the generally ring-shaped energetic material 214 that has the inner opening 215, a generally disk-shaped energetic material can be provided, which does not include the inner opening 215 in an inner portion (e.g. center) of the energetic material. In other examples, instead of providing an energetic material that is generally circular in cross section, energetic materials having other shapes can be employed.

As further shown in FIG. 2A, the perforator charge 112 can include a shock attenuator 222 positioned between the energetic material 214 and the main explosive 204. The shock attenuator 222 can be a layer of shock attenuation material, such as a polymer, plastic, a material containing air spaces or other voids, foam, cork, or any other metallic or non-metallic material of relatively low density. The shock attenuator 222 in some examples can also be generally ring-shaped. The shock attenuator 222 is arranged to cause a delay between the detonation of the explosive 204 and activation of the energetic material 214. This delay allows a perforation tunnel to first be formed by the perforating jet produced by the perforator charge 112, after which activation of the energetic material 214 creates an energy wave for enlarging the perforation tunnel, creating fractures, and/or removing crushed zone damage.

In other implementations, the shock attenuator 222 can be omitted.

In operation, the detonating cord 114 of FIG. 1 is initiated, which causes detonation of the main explosive 204 in the perforator charge 112. Detonation of the main explosive 204 creates a detonation wave that causes the liner 206 to collapse under the detonation force of the main explosive 204. Material from the collapsed liner 206 forms a perforating jet which shoots out through the front opening of the outer case 202 and towards the surrounding structure, which can include the casing/liner 104 and the surrounding subterranean formation.

The collapse of the liner 206 under the detonation force starts near an apex portion 224 of the liner 206, and proceeds to near the base portion 226 of the liner 206. The tip of the perforating jet produced from collapse of the liner 206 is formed by the apex portion 224 of the liner 206, while the tail of the perforating jet is formed by the base portion 226 of the liner 206.

In implementations where the energetic material 214 is generally ring-shaped, the perforating jet extends through the opening 215 (FIG. 3) of the energetic material 214. After some amount of delay caused by the shock attenuator 222, the energetic material 214 is activated, which produces an energy wave. Activation of the energetic material 214 is caused by the detonation wave of the main explosive 204.

As noted above, in different implementations, the energetic material 214 is not ring-shaped as shown in FIG. 3—rather, the energetic material can be generally disk-shaped (without the opening 215 of FIG. 3 in an inner portion, such as a center, of the energetic material). FIG. 2B shows a variant of the perforator charge 112B that includes a generally disk-shaped energetic material. In FIG. 2B, a retaining shell or cap 216B is provided that has a receiving chamber 218B to receive the energetic material 214B. Note that the retaining shell or cap 216B in implementations according to FIG. 2B does not have the protruding portion 220 of FIG. 2A.

In FIG. 2B, a shock attenuator 222B is provided between the main explosive 204 and the energetic material 214B. The shock attenuator 222B in FIG. 2B can be generally disk-shaped, according to some examples.

FIG. 4 is a cross-sectional view of the perforating gun 108 of FIG. 1. A perforator charge 112A is located inside an inner chamber 402 of the housing of the loading tube 110. The perforator charge 112A is similar to the perforator charge 112 of FIG. 2A, except that the energetic material 214A is thicker than the energetic material 214 in the perforator charge 112 of FIG. 2A. Accordingly, the retaining shell 216A of FIG. 4 is slightly enlarged to accommodate the thicker energetic material 214A. The energetic material 214A is similar to the energetic material 214 in that the energetic material 214A is also generally ring-shaped. In different implementations, the energetic material 214A can be generally disk-shaped, or can have another shape.

In FIG. 4, the retaining element 212 at the rear portion of the outer case 202 is bent to hold the detonating cord 114 against the rear portion of the main explosive 204.

FIG. 5 is a flow diagram of a process of using the perforator charge 112, 112A, or 112B of FIG. 2A, 2B, or 4. A perforating gun (e.g. 108 in FIG. 1) having perforator charges is lowered (at 502) into a wellbore. At least one of the perforator charges of the perforating gun is configured according to FIG. 2A, 2B, or 4.

The process then activates (at 504) the perforating gun, which causes detonation of the perforator charges. Detonation of the perforator charges causes respective perforating jets to be produced by the perforator charges, which extend perforation tunnels in the surrounding subterranean formation. The energetic material in the at least one perforator charge configured according to FIG. 2A, 2B, or 4 is then activated, which produces an energy wave.

In some examples, by using the perforator charge 112, 112A, or 112B according to some implementations, both the perforating operations and the post-perforating operations of creating fractures, enlarging a perforation tunnel, and/or reducing crushed zone damage can be performed in a single run using the same tool string (e.g. 100 in FIG. 1). In this manner, improved communication between a wellbore and the surrounding subterranean formation can be achieved.

In the foregoing description, numerous details are set forth to provide an understanding of the subject disclosed herein. However, implementations may be practiced without some or all of these details. Other implementations may include modifications and variations from the details discussed above. It is intended that the appended claims cover such modifications and variations. 

What is claimed is:
 1. A perforator charge comprising: a case; an explosive inside the case; a liner to be collapsed by detonation of the explosive to form a perforating jet; an energetic material to be activated in response to the detonation of the explosive; a shock attenuator between the explosive and the energetic material; and a retaining structure attached to the case to retain the energetic material to the case.
 2. The perforator charge of claim 1, wherein the energetic material includes a discrete segment of the energetic material positioned at an opening of the case through which the perforating jet is to pass.
 3. The perforator charge of claim 2, wherein the discrete segment is generally ring-shaped.
 4. The perforating charge of claim 2, wherein the discrete segment is generally disk-shaped without an opening in an inner portion of the energetic material.
 5. The perforator charge of claim 1, wherein the energetic material is selected from the group consisting of a propellant, a high explosive, gun powder, a combustible metallic powder, thermite, or any combination thereof.
 6. The perforator charge of claim 1, wherein the energetic material is selected from the group consisting of a high explosive, gun powder, thermite, or any combination thereof.
 7. The perforator charge of claim 1, wherein the shock attenuator is generally ring-shaped or generally disk-shaped.
 8. The perforator charge of claim 1, wherein the shock attenuator is to cause a delay between the detonation of the explosive and activation of the energetic material.
 9. The perforator charge of claim 1, wherein the energetic material is positioned at an opening of the case without contacting any part of an outer surface of the case.
 10. The perforator charge of claim 1, wherein the energetic material has an opening through which the perforating jet is to pass, and wherein the energetic material is to be activated after the perforating jet has passed through the opening.
 11. The perforator charge of claim 1, wherein the perforating jet is to pass through the energetic material.
 12. A perforating gun comprising: a carrier structure; and perforator charges attached to the carrier structure, wherein at least one of the perforator charges includes: a case; an explosive inside the case; a liner to be collapsed by detonation of the explosive to form a perforating jet; and a discrete segment of energetic material retained to the case and to be activated in response to the detonation of the explosive, wherein the energetic material is selected from the group consisting of a high explosive, gun powder, thermite, or any combination thereof.
 13. The perforating gun of claim 12, wherein the discrete segment of energetic material is retained to the case without contacting any part of an outer surface of the case.
 14. The perforating gun of claim 12, further comprising a retaining shell that is attached to the case and that receives the discrete segment of the energetic material.
 15. The perforating gun of claim 12, wherein the discrete segment of the energetic material is without any opening in an inner portion of the discrete segment.
 16. The perforating gun of claim 12, wherein the at least one perforator charge further comprises a shock attenuator between the explosive and the discrete segment of energetic material.
 17. A method for use in a well, comprising: lowering a perforator charge into the well, wherein the perforator charge includes: a case; an explosive inside the case; a liner to be collapsed by detonation of the explosive to form a perforating jet; an energetic material to be activated in response to the detonation of the explosive; a shock attenuator between the explosive and the energetic material; and a retaining structure attached to the case to retain the energetic material to the case; and activating the perforator charge to create a perforation tunnel.
 18. The method of claim 17, wherein activating the perforator charge causes detonation of the explosive and collapse of the liner to form a perforating jet for creating the perforation tunnel, where the energetic material is activated after formation of the perforating jet.
 19. The method of claim 18, wherein the energetic material is activated a delay after detonation of the explosive, the delay being caused by the shock attenuator.
 20. The method of claim 17, wherein activating the energetic material causes generation of an energy wave into the perforation tunnel. 